1. Field of the Invention
The present invention relates to a platen cover open/close mechanism for an image scanning device of an image forming apparatus, such as an image scanner or an electrophotographic copier.
2. Description of the Related Art
Conventionally, an image scanning device incorporated in an image forming apparatus like various types of copiers is constructed as shown in FIG. 1. Specifically, the image scanning device is provided with a platen cover 1 for holding an original 4 placed at a specific position on platen glass 3 which serves as an image scanning surface by pressing the original 4 in position in a stable manner. A rear end of the platen cover 1 is usually hinged to the image forming apparatus so that the platen cover 1 can be swung up and down about its hinged end by manually lifting it by a grip 2 provided on its front edge. In FIG. 1, the reference numeral 5 designates an operator panel.
Since the platen glass 3 is usually provided at an uppermost part of the image scanning device, its location often causes inconvenience to a little child or a physically handicapped person confined to a wheelchair when such a person attempts to move the platen cover 1 up and down. In fact, it is occasionally difficult, or even impossible, for them to reach the platen cover 1 provided at the uppermost part for opening and closing it.
Even if they could manage to open and close the platen cover 1 one way or another, closing the platen cover 1 after setting the original 4 in position might produce a wind pressure directed in a particular direction. Consequently, the original 4 once placed in a proper position might be displaced. Particularly when the original 4 is a small-sized sheet, such as a postcard, it can easily be displaced by the influence of the wind pressure, and it is not easy for little children and handicapped persons to make sure that the original 4 is kept in the correct position after closing the platen cover 1.
To overcome the aforementioned problem, Japanese Laid-open Patent Publication No. S62-211633 discloses an arrangement in which a platen cover is made bendable by means of a hinge joining its two divided portions. The hinge extends obliquely to a reference line with which each original should be aligned. In this structure, an operator can easily open, or lift up, one portion of the platen cover and visually check that the original is in proper alignment with the reference line, even when the original is small-sized.
On the other hand, Japanese Laid-open Utility Model Publication No. S63-164742 discloses an arrangement in which an original holding sheet is provided on a bottom surface of a platen cover and, when the platen cover is closed, a squeezer presses the original holding sheet against an original to prevent its displacement. Also, Japanese Laid-open Utility Model Publication No. H1-128234 discloses an arrangement in which a platen cover is opened and closed by an electric motor to provide improved operability.
In any of the aforementioned examples of the prior art, the platen cover is opened and closed by swinging it up and down about its rear end. In these prior art arrangements, opening and closing the platen cover forcibly produces variations in wind pressure near the platen glass, and it is likely that the original is displaced from its correct position due to the influence of the wind pressure. Particularly when the original is small-sized or thin, it can be moved quite easily from the set position by a flow of air. In this circumstance, it has been needed to provide means for preventing this kind of displacement of the original.